TOKYO, April 27 (Xinhua) -- Two knives were found bedside the classroom desk of Prince Hisahito, the 12-year-old grandson of Emperor Akihito, with police saying Saturday they are investigating security footage of an intruder entering the school grounds a day earlier.

Police investigators said the two blades were found in Prince Hisahito's classroom at Ochanomizu University Junior High School in Tokyo's Bunkyo Ward on Friday.

The police said, however, that no students were present in the room at the time the weapons were put there, as they were attending activities elsewhere in the school.

According to video footage taken Friday, a middle-aged man wearing a blue uniform, possibly to disguise himself as a construction worker, and hiding his face with a helmet, entered the school premises.

He is believed by the Metropolitan Police Department here to have left the knives near the classroom desk of Prince Hisahito.

The incident comes less than a month after Prince Hisahito began his studies at the junior high school and ahead of next week's imperial succession.

The imperial succession will mean Prince Hisahito will be second in line to the Chrysanthemum Throne following the abdication of his 85-year-old grandfather, Emperor Akihito, on Tuesday and the enthronement of Crown Prince Naruhito the following day.

Investigators, while searching for the intruder, are also looking into whether the planting of the knives was in any way connected to the current imperial events involving the emperor's abdication and enthronement of Crown Prince Naruhito.